Re: Generators/coroutines in future Ada?

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 12/07/2017 08:35, G.B. wrote:
> On 11.07.17 22:25, Dmitry A. Kazakov wrote:
>> On 2017-07-11 21:22, J-P. Rosen wrote:
>>> Le 11/07/2017 à 20:36, Victor Porton a écrit :
>>>> This state also includes the point of execution (like "We are in the 
>>>> second
>>>> loop in its second operator.")
>>>>
>>>>> This can easily be achieved with a function within a package, where 
>>>>> the
>>>>> package serves to protect and hide the function's state.
>>>> Ada currently has no support to save such (point of execution) states.
>>> It has. Make your generator a task, and have an accept when the data is
>>> ready, which can be nested as deep as you want in any construct.
>>>
>>> A task is a perfect abstraction for a thread of control that maintains
>>> its own execution state!
>>
>> Except that no control is required.
>>
>> I don't understand what is wrong with:
>>
>>    type Stateful is limited private;
>>    function Generate (X : not null access Stateful) return Things;
> 
> Arguably, first, a "function" lacks query/command separation:
> 
>     type Stateful is limited interface;
>     function Current (x : Stateful) return Thing;  -- (*)
>     procedure Next (x : in out Stateful);

I don't understand this example. Why Next cannot be a part of Current? 
Example:

    X := Stack.Pop;

> Not surprisingly, I think, Icon's generators are available to
> use in while-loops that look perfectly ordinary. If Ada requires
> generators to be more explicit:
> 
>     G     : Stateful := Strings.Find
>                (Subject => "...",
>                Pattern => "___");
> 
>     while X of G with condition (X) loop    -- not Ada
>        ...
>     end loop;
> 
> "while ... of ... with" then requires G to be a Stateful.
> Presence of special syntax is, as previously, HOL.

I don't understand this example. If you mean multiple return values 
(tuples), yes Ada should have them, but that is unrelated to stefulness.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de